Astronomers have made an incredible and groundbreaking discovery – a faint star in an extremely tight orbit around Sagittarius A*, the supermassive black hole at the center of the Milky Way.
A series of images taken with the GRAVITY instrument on ESO’s Very Large Telescope Interferometer shows several stars orbiting Sagittarius A*. One of these stars, S301, was recently discovered to pass much closer to the black hole than any other known star. Image credit: ESO / GRAVITY collaboration.
“Sagittarius A* is the nearest supermassive black hole to the galactic center, located 8,300 parsecs away,” said Dr. Karim Abd El Dayem from the Paris Observatory and his research team.
“In this vicinity, we were able to observe the orbits of individual stars around it.”
“This star will serve as a test particle to explore the gravitational potential around a 4.3 million solar mass black hole.”
The newfound star, dubbed S301, was identified in the spring of 2023 using ESO’s Very Large Telescope Interferometer equipped with the GRAVITY instrument.
By tracking its motion forward and examining older data, astronomers confirmed sightings dating back to 2017.
S301 completes its orbit in just 8.7 years, making it the shortest recorded orbital period around Sagittarius A*, and follows a highly elongated orbit, passing within 136 to 142 times the black hole’s Schwarzschild radius at its closest approach.
At this point, the star reaches speeds of about 25,000 km/s, exceeding 8% of the speed of light.
Based on its faintness, astronomers estimate that S301 is a compact, Sun-like star with a mass of approximately 1.1 to 1.5 times that of the Sun. It is too small and dim to be one of the giant stars previously observed near a black hole.
They propose that S301 may have once been part of a close binary star system that ventured too close to Sagittarius A* and was likely torn apart by the black hole’s gravity, a process known as the Hills mechanism.
One star would have been ejected outward as a hypervelocity star, while its companion, S301, would have been trapped in its current tight, elongated orbit.
S301 is so close to Sagittarius A* that it is the first star known to be capable of directly measuring the rotation of a black hole.
According to Einstein’s theory of general relativity, a rotating black hole twists space-time, affecting the orbits of surrounding stars. This effect is more pronounced for objects orbiting a rapidly rotating black hole at close range.
Professor Reinhard Guentzel, Nobel laureate and director of the Max Planck Institute for Extraterrestrial Physics, remarked, “After years of closely monitoring stars orbiting Sagittarius A*, the central black hole of our galaxy, we have made this significant discovery of a highly promising star.”
“S301’s close orbit around Sagittarius A* provides new insights into the fundamental nature of spacetime in this extreme black hole environment.”
“We aim to use this star to measure black hole rotations in the next decade,” said Dr. Felix Mann, a student at the Max Planck Institute for Extraterrestrial Physics.
The discovery of S301 can be found in the following article: paper in the journal nature.
_____
K. Abd El Dayem et al. Discovery of a rotation-sensitive star in Sagittarius A*. naturepublished online on August 19, 2026. doi: 10.1038/s41586-026-10894-w
Source: www.sci.news
